In motor vehicles, distance regulation systems, also known as ACC (Adaptive Cruise Control) systems, are increasingly used that automatically regulate the distance of the own vehicle from a vehicle traveling in front of it. The sensor system has, for example, a radar sensor with which the distances and relative speeds, and generally also the directional angles of vehicles traveling in front can be measured. On the basis of the measured directional angle, a decision can be made as to which of the located vehicles is situated in the same lane as the own vehicle, thus representing a relevant target object for the adaptive cruise control. The goal of the control is typically to maintain a defined setpoint distance from this target object, or at least to avoid falling significantly under this setpoint distance. The setpoint distance is usefully speed-dependent, and is generally defined via a setpoint time gap that indicates the time interval in which the two vehicles pass the same point on the roadway. On the basis of the data measured by the radar sensor, the controller calculates for example a positive or negative setpoint acceleration that is required in order to maintain the setpoint distance, and via the actuator system intervenes in the vehicle's drive train, and also in the vehicle's brake system if required, in a manner corresponding to this setpoint acceleration.
In order to achieve a comfortable system behavior and in order to take into account physical properties of the actuator system, as well as safety-related factors, the setpoint acceleration that is finally outputted to the actuator system is limited by an upper and/or lower limit of intervention. However, this limiting can have the consequence that in critical traffic situations the automatic longitudinal speed controlling or longitudinal acceleration controlling of the own (host) vehicle cannot prevent a collision with the vehicle traveling in front. For this reason, an important component of the known ACC systems is an output device via which a take-over request can be issued to the driver in such cases. In this way, the driver is requested to take over the control of the vehicle himself in order to gain control over the critical situation, the driver not being bound to the intervention limits of the control system. For example, in known systems such a take-over request is issued if the controller calculates a setpoint acceleration that would be required in order to maintain the setpoint distance but that lies outside the limits of intervention of the system. In order to gain control over the critical driving situation, the driver is then generally required to respond to the event in a sufficiently rapid and/or energetic, active manner.